1. Field of the Invention
The present invention relates to a drive device and an alternating current (hereafter, also referred to as AC) power supply device provided with the drive device, and particularly to a drive device driving a plurality of semiconductor elements having respective reference potential electrodes coupled via a main electrode unit as well as an AC power supply device provided with the drive device.
2. Description of the Background Art
A drive device driving semiconductor elements may include, e.g., a plurality of semiconductor elements coupled in parallel. In this structure, a parasitic inductance is present in each of interconnections between the semiconductor elements. Therefore, when the semiconductor element performs a switching operation to supply intermittently an output current, an induced electromotive force occurs in a parasitic inductance.
In a general power semiconductor element, a change rate of current at the time of switching is about 3000 A/μs. Therefore, when the parasitic inductance is 10 nH (nanohenry), the induced electromotive force is equal to (10 n×3000/1μ=30 (V)). This induced electromotive force destroys the semiconductor element, and causes a malfunction of circuits.
International Publication No. WO 01/001555 brochure, Japanese Patent Laying-Open Nos. 2001-043990, 2006-229454, 2003-339152 and 2001-045740, and International Publication No. WO 01/089090 brochure (publications 1-6) have disclosed structures driving semiconductor elements, and particularly structures for preventing a large voltage such as an induced electromotive force that may instantaneously occurs, and thereby preventing destruction and malfunctions of circuits.
For example, the publication 1 has disclosed the following structure. In a power conversion circuit that converts a direct current into an alternating current or the like to supply a power to a load, the disclosed structure aims to prevent a malfunction and destruction due to a surge voltage. This structure includes a level shift circuit that is arranged corresponding to a switching semiconductor element forming a main circuit, and performs level shifting of a reference potential on an output side in a manner following variations in reference potential of the switching semiconductor element. A control signal is transmitted via the level shift circuit to the switching semiconductor element. A direct current control power supply supplying the power to the level shift circuit is connected to a negative pole of the switching semiconductor element via at least one of the inductance and the resistance.
The publication 2 has disclosed the following structure. An output terminal of a bridge drive circuit is connected to gate terminals of four MOS transistors in an H-bridge circuit via resistances. At least one of four MOS transistor drive circuits has an output terminal connected to an interconnection providing a negative-side reference potential via a capacitor. By this structure, an integrating circuit formed of the resistance and the capacitor operates as a filter to prevent application of a high voltage to the MOS transistor drive circuit.
However, the publications 1-6 have not disclosed a structure that is employed in a drive device driving, based on a common drive control signal, a plurality of semiconductor elements having respective reference potential electrodes coupled via a main electrode unit, and reduces an influence of an induced electromotive force caused by a switching operation of the semiconductor element.